OAM Overview
Page 1378 7750 SR OS Services Guide
End-to-End Testing of Paths in an LDP ECMP Network
Figure 4: Network Resilience Using LDP ECMP
Figure 74 depicts faults that are detected through IGP and/or LDP are corrected as soon as IGP and
LDP re-converge. The impacted traffic will be forwarded on the next available ECMP path as
determined by the hash routine at the node that had a link failure.
However, there are faults which the IGP/LDP control planes may not detect. These faults are
mainly due to a corruption of the control plane state or of the data plane state in a node. The LDP
ECMP OAM is intended to detect these “silent” data plane and control plane faults. For example,
it is possible that the forwarding plane of a node has a corrupt Next Hop Label Forwarding Entry
(NHLFE) and keeps forwarding packets over an ECMP path only to have the downstream node
discard them. This data plane fault can only be detected by an OAM tool that can test all possible
end-to-end paths between the ingress LER and the egress LER. A corruption of the NLHFE entry
can also result from a corruption in the control plane at that node.
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